1. Field of the Invention
The present invention relates to an explosion-proof portable gas detector, and particularly to an explosion-proof portable gas detector equipped with a gas sucking means for introducing a gas to be detected into it and capable of detecting plural kinds of gas components.
2. Description of the Background Art
There are generally frequent occasions when it may be possible in, for example, underground job sites or gateways, or other places where persons enter, or working regions that air in an environmental atmosphere is in a dangerous state, or will become a dangerous state, such as occasions when hazardous gases such as carbon monoxide and hydrogen sulfide gases may possibly be contained in air in such an environment, or when the oxygen gas concentration in air may possibly be lowered.
When the air in the environmental atmosphere has become a dangerous state to persons due to high concentration of the dangerous gases contained or low oxygen gas concentration, it is necessary to immediately sense the fact.
From such a demand, there have heretofore been proposed various types of portable gas detectors.
Such a portable gas detector is generally used by being fitted to a person's body by means of, for example, a proper fitting member to carry it together with the person's body by this person. However, static electricity is charged on a housing made of, for example, a resin making up the portable gas detector due to, for example, friction of its surface in a working site, and so there is a possibility that firing may be caused by this static electricity.
The portable gas detector is thus required to have a structure capable of avoiding such a possible hazard, specifically, a structure satisfying, for example, the following conditions (a) to (c):    Condition (a): the degree of an insulation resistance value of a resin making up a portable gas detector is not higher than a certain value;    Condition (b): the extent of a surface area of a continuous portion composed of a resin is not greater than a certain value; and    Condition (c): the degree of a comparative tracking index as an index, for example, to dielectric breakdown resistance in relation with equipment voltage is not lower than a certain value.
The term “comparative tracking index” as used herein means a value measured in accordance with IEC standard 60112 (Method for the determination of the comparative tracking indices and the tracking indices of solid insulating materials under wet conditions).
Various static charge-controlling resin materials have heretofore been proposed as resin materials forming housing (see, for example, Japanese Patent Application Laid-Open No. 2002-309097). However, those satisfying all the above-described conditions (a) to (c) are not known, and a structure, to which a measure against static electricity is taken so as to satisfy the standard of explosion-proofness as to a portable gas detector used under an environment having a danger of catching fire, is formed by, for example, using a resin material satisfying the condition (a) and controlling the extent itself of a surface area of a continuous resin portion of the housing small so as to satisfy the conditions (b) and (c) (see, for example, Japanese Patent Application Laid-Open No. 2000-209250).
In addition, a measure to ensure explosion-proofness is also taken to members surrounding spaces, in which a power source part for supplying power to functional members related to gas detection, and other members having explosive energy are arranged.
For example, a portable gas detector driven by a battery, in which a battery pack obtained by coating all of a plurality of rod-like batteries (storage batteries) and an insulating spacer with a silicone rubber envelope in a state the batteries have been arranged in parallel in such a manner that different poles adjoin each other to be connected in series, and the insulating spacer has been intervened between the batteries is used, whereby a power source part is provided as an explosion-proof structure, is known (see, for example, Japanese Patent Application Laid-Open No. 7901/1996).